summaryrefslogtreecommitdiff
path: root/kernel/locking/rwsem-xadd.c
diff options
context:
space:
mode:
Diffstat (limited to 'kernel/locking/rwsem-xadd.c')
-rw-r--r--kernel/locking/rwsem-xadd.c27
1 files changed, 14 insertions, 13 deletions
diff --git a/kernel/locking/rwsem-xadd.c b/kernel/locking/rwsem-xadd.c
index d6203faf2eb1..7628c3fc37ca 100644
--- a/kernel/locking/rwsem-xadd.c
+++ b/kernel/locking/rwsem-xadd.c
@@ -246,19 +246,22 @@ struct rw_semaphore __sched *rwsem_down_read_failed(struct rw_semaphore *sem)
return sem;
}
+EXPORT_SYMBOL(rwsem_down_read_failed);
static inline bool rwsem_try_write_lock(long count, struct rw_semaphore *sem)
{
- if (!(count & RWSEM_ACTIVE_MASK)) {
- /* try acquiring the write lock */
- if (sem->count == RWSEM_WAITING_BIAS &&
- cmpxchg(&sem->count, RWSEM_WAITING_BIAS,
- RWSEM_ACTIVE_WRITE_BIAS) == RWSEM_WAITING_BIAS) {
- if (!list_is_singular(&sem->wait_list))
- rwsem_atomic_update(RWSEM_WAITING_BIAS, sem);
- return true;
- }
+ /*
+ * Try acquiring the write lock. Check count first in order
+ * to reduce unnecessary expensive cmpxchg() operations.
+ */
+ if (count == RWSEM_WAITING_BIAS &&
+ cmpxchg(&sem->count, RWSEM_WAITING_BIAS,
+ RWSEM_ACTIVE_WRITE_BIAS) == RWSEM_WAITING_BIAS) {
+ if (!list_is_singular(&sem->wait_list))
+ rwsem_atomic_update(RWSEM_WAITING_BIAS, sem);
+ return true;
}
+
return false;
}
@@ -465,6 +468,7 @@ struct rw_semaphore __sched *rwsem_down_write_failed(struct rw_semaphore *sem)
return sem;
}
+EXPORT_SYMBOL(rwsem_down_write_failed);
/*
* handle waking up a waiter on the semaphore
@@ -485,6 +489,7 @@ struct rw_semaphore *rwsem_wake(struct rw_semaphore *sem)
return sem;
}
+EXPORT_SYMBOL(rwsem_wake);
/*
* downgrade a write lock into a read lock
@@ -506,8 +511,4 @@ struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem)
return sem;
}
-
-EXPORT_SYMBOL(rwsem_down_read_failed);
-EXPORT_SYMBOL(rwsem_down_write_failed);
-EXPORT_SYMBOL(rwsem_wake);
EXPORT_SYMBOL(rwsem_downgrade_wake);